Low optical loss polymers

ABSTRACT

A fluorinated polymerizable compound useful for fabricating planar optical devices includes at least one fluorinated alkylene or alkylene ether moiety and at least two terminal acrylate moieties, each terminal acrylate moiety being connected to one of the fluorinated alkylene or fluorinated alklene ether moieties by an ester linking group. The fluorinated polymerizable compounds, or macromers, of this invention are useful for forming optical components exhibiting a refractive index comparable to that of glass fiber waveguides, while also exhibiting very low absorption losses. Polymerizable compositions suitable for preparing optical components can be prepared by combining the macromers of the invention with a photoinitiator. Conventional optical monomers may also be employed, if desired.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/747,068, filed Dec. 21, 2000, now U.S. Pat. No. 6,486,637 the contentof which is relied upon and incorporated herein by reference in itsentirety. The benefit of priority under 35 U.S.C. §120 to theabove-referenced application is hereby claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fluorinated compounds that may bepolymerized to form materials exhibiting low light loss, and to planarwaveguide devices fabricated from polymerizable fluorinated compounds.

2. Technical Background

It is known to fabricate planar waveguide devices such as opticalswitches, variable attenuators, and tunable gratings of polymericmaterials. Polymeric waveguide devices generally comprise a lowercladding layer having a low refractive index, a core layer having a highrefractive index and an upper cladding layer having a low refractiveindex.

A typical method of fabricating waveguide components of polymericmaterials involves depositing a liquid polymerizable composition ontothe surface of a substrate, such as by spin-coating, and subsequentlypolymerizing the deposited coating. Fluorinated acrylate liquid monomershave the advantages of being solvent-free and provide low loss waveguidestructures with very low birefringence. Conventional polymerizablecoating compositions of this type, however, generally have severaldisadvantages. A significant disadvantage with typical compositions isthat the polymerized material usually has a refractive index that issubstantially lower than silica. This results in a mismatch between therefractive index of the polymer waveguide of the planar optical deviceand the silica waveguide of an optical fiber connected to the polymerwaveguide. This mismatch of the refractive indexes increases couplinglosses at the interface between the waveguides, and can also lead tounwanted reflection of a guiding optical signal at the interfaces ofwaveguide and fiber. The relatively low refractive index of typicalpolymers used in planar optical components is caused by the use offluorinated monomers. The fluorinated monomers can be used to reduce thevolume density of carbon-hydrogen bonds in polymeric optical materialsand thereby reduce absorption losses associated with the vibration modesof these carbon-hydrogen bonds. Thus, although coupling losses betweensilica optical fibers and polymer waveguides can be reduced by loweringthe concentration of fluorinated monomers, this would cause anundesirable, increase in absorption losses. Therefore, it would bedesirable to provide polymeric coating compositions that can bepolymerized to form optical components having a refractive index moreclosely matched to the refractive index of silica, without increasingabsorption losses.

Another disadvantage with conventional coating compositions used to formpolymeric optical components is that the viscosity of such compositionsis undesirably low, typically less than 100 centipoise. This lowviscosity imposes constraints on the thickness of a single layer thatcan be applied by spin-coating. In addition, very low viscositymaterials will sometimes flow along and/or from the surface of asubstrate or previously spin-coated layer resulting in uneven coatingthickness. This is undesirable because planar waveguides comprised oflayers having a non-uniform thickness exhibit increased loss of lightand other undesirable optical behavior. Therefore, polymerizablecompositions having a relatively higher viscosity would be desirable forfabrication of planar waveguide devices.

Another problem with conventional polymerizable compositions used tofabricate planar waveguide devices is that the lower molecular weightmonomers typically used in such compositions exhibit significantvolatility, especially when the composition is exposed to a high vacuum.Typical polymerizable compositions used for fabricating planar waveguidedevices include a monomer blend in which the various monomer componentsin the blend have different relative volatilities. As a result, theconcentration of the various monomer components can change duringprocessing steps, such as spin coating and polymerization. Becauserelatively thin layers (e.g., typically from about 2 microns to about 10microns) are deposited during fabrication of a planar waveguide device,the compositional changes caused by the different relative volatilitiesof the monomer components can be relatively severe, profoundly degradingthe ability to control the refractive index of the polymerized material.It is often desirable to polymerize the coating compositions under avacuum or under a nitrogen blanket to eliminate the presence of oxygenduring polymerization. In such cases, even a relatively low volatilitymakes it especially difficult to control the processes necessary toensure that the coating has the composition required to achieve adesired refractive index. Volatile monomers also adversely affect theability to use proximity printing processes (photolithographic processesin which a mask is spaced from the substrate during the radiationexposure step), since the volatile monomers can fog the mask during theprinting process.

Accordingly, it would be highly desirable to provide polymerizablecompositions for fabricating planar waveguide devices that exhibit amore favorable range of viscosities, with a lower volatility, and whichcan be polymerized to form a waveguide material that exhibits low lightabsorption losses and which has a refractive index that is closer to therefractive index of a silica optical fiber. More specifically, it wouldbe desirable to provide fluorinated polymerizable compounds that exhibita selected range of viscosities, low volatility, and that can bepolymerized to form a material having a refractive index that moreclosely matches the refractive index of optical fibers.

SUMMARY OF THE INVENTION

The invention provides fluorinated compounds that overcome problemsassociated with conventional compositions used for fabricating polymericwaveguides. More specifically, the invention provides fluorinatedcompounds that may be polymerized to form materials exhibiting a higherrefractive index that is more closely matched to that of a silicawaveguide, while also achieving low absorption losses. The fluorinatedcompounds may also be used in coating compositions that have higherviscosities that are favorable for fabricating relatively thick layersof uniform thickness. The fluorinated compounds of this invention mayalso be used for preparing coating compositions having a relatively lowvolatility, whereby the fabrication of devices having a desiredrefractive index is more easily controllable, and which facilitatesproximity printing.

In accordance with an aspect of the invention, the fluorinated compoundcomprises at least one fluorinated alkylene or alkylene ether moiety,and at least two terminal acrylate moieties. Each of the terminalacrylate moieties is connected to the fluorinated alkylene orfluorinated ether moiety or moieties by an ester (—CO₂—) linking group.

The invention also pertains to polymerizable compositions containing thefluorinated compounds, and to planar waveguide devices fabricated fromsuch compositions.

Additional features and advantages of the invention will be set forth inthe detailed description which follows and will be apparent to thoseskilled in the art from the description or recognized by practicing theinvention as described in the description which follows together withthe claims and appended drawings.

It is to be understood that the foregoing description is exemplary ofthe invention only and is intended to provide an overview for theunderstanding of the nature and character of the invention as it isdefined by the claims. The accompanying drawing is included to provide afurther understanding of the invention and is incorporated andconstitutes part of this specification. The drawing illustrates variousfeatures and embodiments of the invention, which, together with theirdescription serve to explain the principals and operation of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section of one example of a planar waveguidedevice of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The fluorinated compounds of this invention are multifunctionalmacromolecules that may be prepared by esterification reactions ofpolyfunctional organic acids, such as dicarboxylic acids, with polyols,such as diols. The esterification product may comprise generally anynumber of polyols and polycarboxylic acids. For example, a species whichis the reaction product of a diol and two dicarboxylic acids can beprepared in high yields under appropriate conditions (e.g. reactantconcentrations, temperature, etc.). Alternatively, appropriatetechniques may be employed to form oligomeric chains of generally anydesired length comprising alternating diols and diacid units. Further,trifunctional, tetrafunctional and other multifunctional polyols andpolycarboxylic acids may be employed to provide branched structures.These esterification products may be terminated with either a hydroxylgroup or a carboxylic acid group. The hydroxyl terminated reactionproducts may be reacted with a carboxyl functional acrylate. Suitablecarboxyl functional acrylates include acrylic acid, methacrylic acid,acrylic acid esters containing a carboxylic acid group (—COOH),methacrylic acid esters containing a carboxylic acid group, as well asthe corresponding acid chlorides (compounds having a —COCl group).Polyol-polycarboxylic acid reaction products having carboxlic acidterminals may be reacted with hydroxy functional acrylates, such ahydroxy ethyl acrylate (HEA).

Examples of suitable polycarboxylic acids include chlorendic diacid,isophthalic acid, tetrachlorophthalic acid, tetrabromophthalic acid,pyromellitic acid, various perfluoroalkyl acids such as those having thegeneral formula HO₂ C(CF₂)_(n) CO₂H, benzene tricarboxylic acid andvarious alkyl dicarboxylic acids having the general formula(CH₂)_(n)(CO₂H)₂ (including succinic acid, glutaric acid, adipic acid,maleic acid and fumaric acid), phthalic acid, terephthalic acid,tetrafluorophthalic acid, benzene tetracarboxylic acid, ethanetricarboxylic acid, propane tricarboxylic acid, butane tetracarboxylicacid and cyclohexanehexacarboxylic acid. The corresponding acidchlorides may be used rather than the acids. For example, the desiredproduct can be obtained by reacting polyfunctional acid chlorides,(e.g., isophthaloyl dichloride) with a suitable polyol.

Examples of suitable polyols include octafluorohexanediol,dodecafluorooctanediol, hexadecafluorodecanediol, as well as variousfluorinated diols available from Ausimont S.P.A. under the nameFLUOROLINK®. FLUOROLINK® D and FLUOROLINK® D1000 have the generalstructure: OCH₂ CF₂ O(CF₂ CF₂O)_(m)(CF₂O)_(n)CF₂ CH₂ OH. FLUOROLINK® Dhas a molecular weight of about 2000, and FLUOROLINK® D1000 has amolecular weight of about 1000. Other examples of suitable polyolsinclude fluorinated diols with the following structure:HOCH₂(CF₂OCF₂)_(x)CH₂ OH, where x is an integer. Specific examplesinclude fluorinated triethylene glycol (x=2) and fluorinatedtetraethylene glycol (x=3). Fluorinated diols of this type arecommercially available from Exfluor Research Corp.

Examples of acrylates that may be reacted with hydroxyl terminatedesters to form polymerizable fluorinated compounds in accordance withthis invention include acrylic acid and methacrylic acid, as well as thecorresponding acid chlorides (e.g., acryloyl chloride). An example of asuitable acrylate that may be reacted with a carboxylic acid orcarboxylic acid chloride terminal group to form polymerizablefluorinated compounds in accordance with the invention includehydroxyethyl acrylate.

Other polymerizable fluorinated compounds encompassed by this inventioninclude acrylate derivatives of carbonates. Examples of compounds ofthis type can be prepared by reacting a polyol with a compound having aplurality of chloroformate (—OCOCl) groups. The reactants are connectedthrough a carbonate (—OCO₂—) linkage to form a carbonate product. Theproduct may have hydroxyl terminals or chloroformate terminals, and maybe either linear or branched. The resulting carbonate product is reactedwith an acrylate to form an acrylate derivative of a carbonate. Examplesof suitable chloroformate compounds include hexafluorobisphenol Abischloroformate, tetrabromohexafluorobisphenol A bischloroformate, andpropane bischloroformate. Examples of suitable polyols include thoselisted above. Other suitable polyols include hexafluorobisphenol A.

Examples of acrylates that can be reacted with hydroxyl-terminatedcarbonates include carboxylic acid functional acrylates such as acrylicacid, methacrylic acid, as well as the corresponding acid chlorides.Examples of acrylates that can be reacted with the chloroformateterminated carbonates include hydroxyl functional acrylates such ashydroxyethylacrylate and dihydroxypropylmethacrylate.

The polymerizable fluorinated polyester acrylates made with fluorinatedpolyols may be represented by the general formula:

where B_(d) is a moiety represented by the formula: R—(CO₂—)₂, B₁ andeach B₂ are moieties independently represented by the general formula:R—(CO₂—) where i is an integer from 2 to 6, each R is independently anaromatic or aliphatic moiety that is optionally halogenated, n, m and Lare integers, at least on of L and m is greater than zero, g and h areintegers from 0 to 10, A is represented by the formula CY₂=CC(X)—CO₂—,where Y is H or D, X is H, D, F, Cl or CH₃, W is represented by one ofthe formulae:

where r is an integer greater than or equal to 2, each R_(f) isindependently represented by one of the formulae —CH₂ (CF₂)_(t)CH₂—,—CH₂ CF₂O—[(CF₂ CF₂ O)_(p)—(CF₂ O)_(q)]—CF₂ CH₂—, —CH₂CH₂OCH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂ O)_(q)]—CF₂CH₂OCH₂CH₂—, or—CH₂CF(CF₃)O(CF₂)₄O[CF (CF)CF₂O]_(p)CF(CF₃)CH₂—, where k, p, q, and tare integers and q can optionally be zero.

Examples of B_(d), B₁ and B₂ may be selected from the polycarboxylicacids and corresponding acid chlorides described above. The R_(f) groupsare derived from the corresponding fluorinated diols. Examples ofsuitable fluorinated polyols that may be used include those describedabove.

Polymerizable fluorinated polyester acrylates prepared from fluorinateddiacids may be represented by the general formula:

(A)_(r)-D₁-(R_(f)-((D_(d)—R_(f))_(g)-D₂-(A)_(u))_(t)

where each D_(d) is independently a moiety with the general structureR—(CH₂O—)₂, where each R is independently an aliphatic or aromaticmoiety that is optionally halogenated, D₁ and each D₂ are independentlymoieties with the general structure R′—(CH₂O—)_(i), where each R′ isindependently an aliphatic or aromatic moiety that is optionallyhalogenated, i is an integer from 2 to 6, A is represented by theformula CY₂═C(X)—C(O)—, where Y is H or D, X is H, D, F, Cl or CH₃, eachR_(f) is independently represented by one of the formulae:—(O)C—(CF₂)_(n)—C(O)—, —(O)C—CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂—C(O)—or—(O)C—CF(CF₃)O(CF₂)₄O[CF(CF₃)CF₂O]_(p)CF(CF₃)—C(O)—, where g, n, p, q,r, u and t are integers, with at least one of r and t being a positiveinteger and q can optionally equal zero Examples of D_(d), D₁ and D₂ maybe derived from ethylene glycol, propylene glycol, butanediol,pentanediol, hexanediol, heptanediol, octanediol, catechol, hydroquinoneand tetrafluorohydroquinone. Examples of D, and D₂ include glycerine,butanetriol, sucrose, pentaerythritol, pyrogallol and phloroglucinol.The R_(f) groups are derived from polycarboxylic acids or thecorresponding acid chlorides. Examples include tetrafluorosuccinic acid,hexafluoroglutaric acid, octafluoroadipic acid, dodecafluorosubericacid, tetradecafluoroazelaic acid, and FLUOROLINK® C (available fromAusimont). FLUOROLINK® C has the structure:

HO₂C—CF₂O—[(CF₂CF₂O)_(p)—(CF₂ O)_(q)]—CF₂—CO₂H

Other examples are fluorinated diacids or the corresponding acidchlorides with the following structure: HO₂C(CF₂OCF₂)_(x)CO₂H, where xis an integer. Specific examples includePerfluoro-3,6-dioxaoctane-1,8-dioic acid (x=2) andPerfluoro-3,6,9-trioxaundecane-1,11-dioic acid (x=3). Fluorinateddiacids of this type are commercially available from Exfluor ResearchCorp. The acrylates derivatives of carbonates made with fluorinateddiols may be represented by the general formula:

Each E_(d) is independently a moiety with the general structureR—(OCO)₂—)₂, where each R is independently an aliphatic or aromaticmoiety that is optionally halogenated, E₁ and each E₂ are independentlymoieties with the general structure of R′—(OCO₂—), where each R′ isindependently an aliphatic or aromatic moiety that is optionallyhalogenated, and i is an integer from 2 to 6, n, m and L are integers,at least one of L and m is greater than zero, g and h are integer from 0to 10, and k is a positive integer.

A is represented by the general formula CY₂═C(X)—CO₂—, where Y is H orD, X is H, D, F, Cl or Ch₃, each W is independently represented by oneof the general formula:

where r is an integer greater than or equal to 2, each R_(f) isindependently represented by one of the formulae —CH₂(CF₂)_(t)C₂—,—CH₂CF₂O—[(cf₂cf₂o)_(p)—(CF₂O)_(q)]—CF₂CH₂—,—CH₂CH₂OCH₂CF₁CF₂O—[(CF₂CF₂O_(p)—(CF₂O)_(q)]—CF₂CH₂OCH₂CH₂—, or—CH₂CF(cf₂)₄O[CF(CF₃)CF₂O]_(p)CF(CF₃)CH₂—, where p, q and t are integersand q can optionally be zero.

Polycarbonates of these types could be derived by reacting aliphatic oraromatic chloroformates with the fluorinated alkyl or fluorinated etherdiols mentioned previously and then forming the acrylate. Examples ofthese chloroformates would include phenylene bischloroformate, bisphenolA bischloroformate, hexafluoro bisphenol A bischloroformate,hexanebischloroformate, tripropylene glycol bischloroformate, chlorendicbischloroformate, and trimethylolpropane trichloroformate.

Polycarbonates of this type could also be derived by reacting thefluorinated alkyl diols or fluorinated ether diols with phosgene togenerate the corresponding chloroformate. These chloroformates couldthen be reacted with aliphatic or aromatic polyols to generate apolycarbonate, which could then be acrylated. Suitable chloroformatesformed in this manner could include octafluorohexanebischloroformate,dodecafluorooctanebischloroformate,hexadecafluorodecanebischloroformate, and bischloroformates, made fromFLUOROLINK® D, FLUOROLINK® D1000 and FLUOROLINK® E from Ausimont, andbischloroformates made from fluorinated triethylene glycol andfluorinated tetraethylene glycol from Exfluor.

Suitable aliphatic or aromatic polyols could include ethylene glycol,propylene glycol, butanediol, pentanediol, hexanediol, heptanediol,octanediol, catechol, hydroquinone, and tetrafluorohydroquinone,glycerine, butanetriol, sucrose, pentaerythritol, pyrogallol, andphloroglucinol, chlorendic diol.

The polymerizable fluorinated compounds of this invention (i.e., thefluorinated polyester acrylates and acrylate derivates of carbonates)typically have a molecular weight of from about 1,000 to about 10,000,and preferably from about 2,000 to 6,000. Such compounds may be regardedas macromers or macromolecular mononers. The macromers of this inventionhave much higher viscosity than the monomers employed in conventionalcompositions used for preparing polymeric optical components. Typically,the macromers of this invention have a viscosity (as determined at 25°C. using a Gilmont falling ball viscometer in accordance with ASTM1343-93) of at least 100 centipoise up to several thousand centipoise(e.g., 5,000 centipoise).

The fluorinated acrylate monomers of this invention are useful forpreparing polymerizable compositions, such as polymerizable compositionsthat polymerize upon exposure to ultraviolet radiation. Suchcompositions may be prepared by combining the monomers of this inventionwith a suitable photoinitiator. The photoinitiator may be used in aconventional amount, with a typical amount being from about 0.5% byweight to about 5% by weight of the composition. Preferably, thepolymerizable compositions are free of solvents, (i.e., the compositionconsists essentially of polymerizable compounds (monomers) and thephotoinitiator). In order to achieve the beneficial effects of higherviscosity, increased refractive index, and reduced volatility, thecomposition should contain at least 1% of the fluorinated monomers ofthis invention by weight, more preferably, at least 5% or 10%, and evenmore preferably at least about 20%. Up to 100% of the monomers in thecomposition may be fluorinated polyester acrylates and/or fluorinatedacrylate derivates of carbonates in accordance with the invention.However, the polymerizable compositions of this invention may alsocontain conventional lower molecular weight monomers (includingmonofunctional and polyfunctional monomers).

The compositions of this invention are useful for fabricating planarwaveguide devices. An example of a planar waveguide device is shownschematically in FIG. 1. The device 10 includes a substrate 12, whichmay, for example, be a silicon wafer, an undercladding layer 14, a corelayer 16 and an overcladding layer 18. Core layer 16 is typically apatterned layer that defines a waveguide circuit. Cladding layers 14 and18 typically surround core layer 16 and have a refractive index that islower than the refractive index of core layer 16. The polymerizablecompositions of this invention that contain the fluorinated polyesteracrylates and/or fluorinated acrylate derivatives of carbonates may beused for forming any or all of layers 14, 16 and 18. It is also possibleto form other waveguiding structures from the materials of thisinvention, as for example, raised-rib, strip-loaded, and slabwaveguides. As is well known in the art, a desired refractive index canbe achieved by selecting monomers having an appropriate level offluorination or other functionality. For example, higher levels offluorination result in lower refractive index, whereas monomers havingchlorine-containing moieties, bromine-containing moieties orphenyl-containing moieties have higher refractive index. Differentmonomers can be blended to provide generally any desired refractiveindex.

An undercladding layer 14 can be formed from the compositions of thisinvention by spin-coating such composition onto substrate 12, andthereafter polymerizing the composition, such as by exposing thecomposition to ultraviolet radiation. A layer 16 using a composition inaccordance with the invention may be prepared by spin-coating acomposition, which polymerizes to form a transparent material having aslightly higher refractive index. After layer 16 has been applied by,for example, spin coating, layer 16 may be patterned using any ofseveral photolithography and etching techniques. Such photolithographytechniques include contact, projection, and proximity lithography. Suchetching techniques include solvent or wet chemical etching, reactive ionetching (RIE), electron beam, and ion milling. Thereafter, a compositionsimilar to that used to form undercladding layer 14 may be depositedover the patterned core layer 16 and polymerized to form overcladdinglayer 18.

EXAMPLES

The following examples illustrate particular embodiments of theinvention, but do not limit the scope of the invention.

Measurements

Each of the materials listed below was tested after synthesis todetermine its suitability for use in making waveguides using thefollowing criteria.

Absorbance

These materials need to be able to be relatively transparent to light at1550 nanometers. To determine this property, the liquid material wasplaced in a 1 centimeter quartz cuvette. A Cary 5 spectrophotometer wasset to zero absorbance in air at 1550 nanometers. The sample was theninserted into the spectrophotometer and the absorbance was measured atthis wavelength. It is preferable that the sample in the cuvette has anabsorbance of less than 0.080. It is more preferable that it has anabsorbance of less than 0.060. It is most preferable that it has anabsorbance of less than 0.050.

Conversion of absorbance measurements at 1550 nanometers to lossmeasurements is possible by correcting for Fresnel reflections using therefractive index of the liquid at 1550 nanometers. The following tableshows the baseline absorbance predicted by Fresnel reflections at agiven refractive index.

Refractive Index Range Baseline Absorbance 1.31-1.33 0.031 1.34-1.380.030 1.39-1.50 0.029 1.51-1.56 0.030 1.57-1.60 0.031

Conversion to loss measurements can then be accomplished with thefollowing equation:

Loss in dB/cm=10·(Measured Absorbance—Baseline Absorbance)

Since the liquid loss measurements for these types of materialscorrespond well to their waveguide losses, the waveguide loss can easilybe estimated. Using an average baseline absorbance value of 0.030, it ispreferable that the loss of these materials as calculated above is lessthan 0.50 dB/cm. It is more preferable that the loss is less than 0.30dB/cm. It is most preferable that the loss is less than 0.20 dB/cm. Fordemanding applications where long lengths are required, it is mostpreferable for the loss to be less than 0.15 dB/cm.

Density

Density was determined using a midget weight-per-gallon cup fromBYK-Gardener USA in accordance with the manufacturer's instructions. Thevalue obtained in pounds per gallon was then converted to grams percubic centimeter.

Viscosity

The viscosity of the monomers was measured at 25° C. using a Gilmontfalling ball viscometer in accordance with ASTM 1343-93. The densitymeasured as described above was used to convert the reading fromcentistrokes to centipoise. Typically, higher viscosity monomers haveimproved spin-coating characteristics.

Refractive Index

The sample was mixed with 2% fluorinated photoinitiator (see below) andfiltered using a 0.1 micron filter. About 1 ml of sample was then placedon top of a silicon wafer resting on a chuck for a spin coater. Thesample was then spun at a speed sufficient to obtain a layer between 5and 7 micron thick of the uncured material on top of the silicon wafer.The assembly was then placed in a nitrogen purge box. The sample waspurged with a heavy flow of nitrogen for two minutes. The sample wasthen cured with 10 milwatts/cm² of UV light from an Oriel model 81173 UVexposure unit for 180 seconds. The high dosage was used to insure thatthe reaction was fully completed. The refractive index of the fullycured film was then measured using a Metricon 2010 prism-coupling devicein accordance with the manufacturer's instructions. All measurementswere made using a 1550 nanometer laser.

Film Uniformity

The sample prepared during the refractive index measurement was thenvisually examined by placing it at an angle to a monochrome lightsource. The sample was judged subjectively on its coating uniformity andthe number of defects (pinholes, orange peel, gel particles, etc.).

Fluorinated Photoinitiator

Since most conventional photoinitiators are not soluble in highlyfluorinated materials, it is necessary to use a photoinitiator thatcontains a flurorinated moiety

Examples of fluorinated photoinitiators can be found in U.S. Pat. Nos.5,391,587 and RE 35,060. In accordance with U.S. Pat. No. 5,391,587, afluorinated photoinitiator was made with the following structure:

To make this material, 23.8 grams (0.1 moles) of Irgacure 2959 (CibaAdditives) was added to a three neck flask equipped with a condenser anda mechanical stirrer. 50 grams (0.12 moles) of perfluorooctanoic acidchloride (Lancaster Synthesis) were then added and the mixture wasstirred and heated to 70° C. for two hours. The IR spectrum was thenchecked every hour until it showed a constant ratio of net absorbancebetween the OH peak at 3450 cm⁻¹ and the carboxyl peak at 1780 cm⁻¹. Thesample was then rotovaped at 85° C. to remove excess perfluorooctanoicacid chloride. The final product was a waxy solid with a melt point ofabout 40° C.

Comparative Example A

CH₂═CHCO₂CH₂CF₂ O(CF₂ CF₂ O)_(m)(CF₂O)_(n)CF₂CH₂O₂CCH═CH₂(Mw≈1100)

A three-neck flask was fitted with a condenser and a mechanical stirringrod. 500 grams (0.5 moles) of FLUOROLINK® D 1000 (Ausimont USA) wasadded to the flask along with 100 grams (1.1 moles) of acryloyl chlorideand 0.5 grams of butylated hydroxy toluene (BHT). The mixture wasstirred vigorously and allowed to exotherm to 70° C. After 4 hours, theexcess acryloyl chloride was stripped off in a rotovap under vacuum andreturned to a clean three-neck flask. 82 grams (0.81 moles) of triethylamine were slowly added while cooling with ice water. A whiteprecipitate rapidly formed. The reaction was allowed to continueovernight. The next day, the material was washed three times with anequal volume of water. The resultant material was a low viscosity liquidwith a slightly yellow color. Test results are shown below:

Absorbance 0.049 Density 1.66 Viscosity 16 cps Refractive Index 1.339Film Uniformity Poor-many defects

While the loss value for this material, as indicated by the lowabsorbance measurement, was very good, its coating properties were verypoor. With a viscosity of only 16 centipoise, the material tended todewet the surface of the silicon wafer. Consequently, coatingnon-uniformities was abundant. For this reason, this material wasunsuitable by itself for use in making waveguides.

Comparative Example B

CH₂═CHCO₂CH₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CH₂O₂CCH═CH₂(Mw≈2100)

A three-neck flask was fitted with a condenser and mechanical stirringrod. 1000 grams (0.5 moles) of FLUOROLINK® D (2000 molecular weight,Ausimont USA) was added to the flask along with 100 grams (1.1 moles ofacryloyl chloride and 1.0 grams of butylated hydroxy toluene (BHT). Themixture was stirred vigorously and allowed to exotherm to 70° C. After 4hours, the excess acryloyl chloride was stripped off in a rotovap undervacuum and returned to a clean three-neck flask. 82 grams (0.81 moles)of triethyl amine were slowly added while cooling with ice water. Awhite precipitate rapidly formed. The reaction was allowed to continueovernight. The next day, the material was washed three times with anequal volume of methanol. The resultant material was a low viscosityliquid with a slightly yellow color. Test results are shown below:

Absorbance 0.042 Density 1.75 Viscosity 43 cps Refractive Index 1.3079Film Uniformity Fair-some, defects

While the loss value for this material, as indicated by the lowabsorbance measurement, was very good, its coating properties were alsopoor. With a viscosity of only 43 centipoise, the material still tendedto dewet the surface of the silicon wafer. Consequently, coatingnon-uniformities were abundant. For this reason, this material wasunsuitable by itself for use in making waveguides.

Example #1

Where RF is CF₂O(CF₂CF₂O)_(m)(CF₂O) CF₂ with a molecular weight of 1000.This material was made as follows: A three-neck flask was fitted with acondenser and a mechanical stirring rod. 125 grams (0.125 moles) ofFLUOROLINK® D1000 was added to the flask along with 12.8 grams (0.063moles) of isophthaloyl dichloride (Aldrich) and 0.15 grams of butylatedhydroxy toluene (BHT). The mixture was heated to 50° C. until allingredients were dissolved. 29 grams (0.29 moles) of triethyl amine werethen added dropwise while maintaining a temperature of between 50° and70° C. using an ice bath. A white precipitate quickly formed. 13.4 gramsof acryloyl chloride (0.15 moles) were added dropwise while stillmaintaining a temperature of between 50° and 70° C. using an ice bath.After 2 hours, the material was washed three times with an equal volumeof methanol and then rotovaped at 70° C. for one hour under vacuum. Testresults are shown below:

Absorbance 0.056 Density 1.70 Viscosity 409 cps Refractive Index 1.3393Film Uniformity Good-no defects

Example #2

Where RF is CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂ with a molecular weight of1000. This material as made as follows: A three-neck flask was fittedwith a condenser and a mechanical stirring rod. 100 grams (0.1 moles) ofFLUOROLINK® D1000 was added to the flask along with 6.8 grams (0.0256moles) of 1,3,5-Benzenetricarbonyl trichloride (Aldrich) and 0.1 gramsof butylated hyroxy toulene (BHT). The mixture was heated to 70° C.until all ingredients were dissolved. The IR spectrum was then checkedevery hour until it showed a constant ratio of net absorbance betweenthe OH peak at about 3500 cm⁻¹ and the carbonyl peak at about 1750 cm⁻¹.22 grams (0.158 moles) of triethyl amine were then added dropwise whilemaintaining a temperature of between 50° and 70° C. using an ice bath. Awhite precipitate quickly formed. 13 grams of acryloyl chloride (0.144moles) were added dropwise while still maintaining a temperature ofbetween 50° and 70° C. using an ice bath. After 2 hours, the materialwas washed three times with an equal volume of methanol and thenrotovaped at 70° C. for one hour under vacuum.

In this reaction, an excess of FLUOROLINK® D1000 was used to preventexcessive chain extension. The final product can be considered to be 3parts of the structure drawn above along with 1 part of the materialfrom comparative example A. Test results are shown below:

Absorbance 0.054 Density 1.70 Viscosity 136 cps Refractive Index 1.3336Film Uniformity Good-no defects

Example #3

Were RF is CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂ with a molecular weight of1000. This material was made as follows: A three-neck flask was fittedwith a condenser and a mechanical stirring rod. 75.8 grams (0.0379moles) of FLUOROLINK® D1000 was added to the flask along with 15.4 grams(0.0758 moles) of isophthaloyl dichloride (Aldrich), 8.8 grams (0.0758)of hydroxyethyl acrylate (Aldrich), and 0.1 grams of butylated hydroxytoluene (BHT). Also added were 50 ml of HFE-7200, a fluorinated solventmade by 3M. The mixture was heated to 70° C. for one hour. 16 grams(0.16 moles) of triethyl amine were then added dropwise whilemaintaining a temperature of between 50° and 70° C. using an ice bath. Awhite precipitate quickly formed. After 2 hours, the material was washedthree times with an equal volume of methanol and then rotovaped at 70°C. for one hour under vacuum. Test results are shown below:

Absorbance 0.040 Density 1.75 Viscosity 4237 cps Refractive Index 1.3289Film Uniformity Excellent-no defects

It will become apparent to those skilled in the art that variousmodifications to the preferred embodiment of the invention as describedherein can be made without departing from the spirit or scope of theinvention as defined by the appended claims.

Example #4

Where RF is CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂ with a molecular weight of2000. This material was made as follows: A three-neck flask was fittedwith a condenser and a mechanical stirring rod. 100 grams (0.05 moles)of FLUOROLINK® D2000 was added to the flask along with 23.2 grams (0.20moles) of hydroxyethyl acrylate (Aldrich), 27.5 grams (0.10 moles) of1,3,5-benzenetricarboxylic acid chloride (Acros) and 0.10 grams ofbutylated hydroxytoluene (BHT). The mixture was heated to 70° C. for 3hours. 130 ml of HFE-7200, a partially fluorinated solvent made by 3Mwas added. 30 grams (0.30 moles) of triethyl amine were then addeddropwise while maintaining a temperature of between 50° and 70° C. usingan ice bath. A white precipitate quickly formed. After 3 hours, thematerial was washed three times with an equal volume of methanol andthen filtered at 0.2 micron. Filtered material was rotovaped at 70° C.for two hours under vacuum. Test results are shown below:

Absorbance 0.047 Density 1.70 Viscosity >5000 cps Refractive Index1.3474 Film Uniformity Good-no defects

Example #5

Where RF is CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂ with a molecular weight of1000. This material as made as follows: A three-neck flask was fittedwith a condenser and a mechanical stirring rod. 40 grams (0.04 moles) ofFLUOROLINK® D1000 was added to the flask along with 10.0 grams (0.023moles) of 1,4,5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic acidchloride and 0.05 grams of butylated hydroxytoluene (BHT). The mixturewas heated to 70° C. until all ingredients were dissolved. 12 ml (0.086moles) of triethyl amine were then added dropwise while maintaining atemperature of between 50° and 70° C. using an ice bath. After reactedfor 1 hour, 6.5 grams of acryloyl chloride (0.07 moles) were addeddropwise while still maintaining a temperature of between 50° and 70° C.using an ice bath. After 3 hours, 80 ml of HFE-7200 was added. Themixture was washed three times with an equal volume of methanol-water(1:5 by volume). Material was filtered at 0.2 micron and then rotovapedat 70° C. for one hour under vacuum. Test results are shown below:

Absorbance 0.052 Density 1.65 Viscosity 285 cps Refractive Index 1.3374Film Uniformity Good-no defects

The invention claimed is:
 1. A compound comprising: at least onefluorinated alkylene or alkylene ether moiety; at least two terminalacrylate moieties; and at least two ester linkages which are not asubunit of an acrylate group.
 2. The compound of claim 1, represented bythe general formula:

where each B₄ is independently a moiety with the general structure R—(CO₂—) ₂, each R is an aromatic or aliphatic group that is optionallyhalogenated, B₁ and each B₂ are independently moieties with the generalstructure of R′—(CO₂—)_(i), where each i is independently an integerfrom 2 to 6, each R′ is independently an aromatic or aliphatic moietythat is optionally halogenated, n, m and L are integers, at least one ofL and m is greater than zero, each g and h is independently an integerfrom 0 to 10, each A is independently represented by the formula CY₂═C(X)—CO₂—, where Y is H or D, X is H, D, F, Cl or CH₃, each W isindependently represented by one of the formulae:

where r is an integer greater than or equal to 2, R_(f) is representedby one of the formulae: —CH₂ (CF₂)_(t)CH₂—,—CH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂ CH₂—, —CH₂ CH₂ OCH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂ CH₂ OCH₂CH₂—, or—CH₂CF(CF₃)O(CF₂)₄O[CF(CF ₃O]_(p)CF(CF₃)CH₂—, where k, p, q and t areintegers and q can optionally equal zero.
 3. The compound of claim 1,represented by the general formula:(A)_(r)-D₁-(R_(f)-((D_(d)—R_(f))_(g))-D₂-(A)_(u))_(t) where each D_(d)is independently a moiety with the general structure R—(CH₂ O—)₂, whereeach R is independently an aliphatic or aromatic moiety that isoptionally halogenated, D₁ and each D₂ are independently moieties withthe general structure R′—(CH₂O—)_(i), where each R′ is independently analiphatic or aromatic moiety that is optionally halogenated, and i is aninteger from 2 to 6, A is represented by the formula CY₂═C(X)—C(O)—,where Y is H or D, X is H, D, F, Cl or CH₃, each R_(f) is independentlyrepresented by one of the formulae: —(O)C—(CF₂)_(n)—C(O)—,—(O)C—CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂—C(O)—, or—(O)C—CF(CF₃)O(CF₂)₄O[CF(CF₃)CF₂O]_(p)CF(CF₃)—C(O)—, where g, n, p, q,r, u and t are integers, with at least one of r and t being a positiveinteger and q can optionally equal zero.
 4. The compound of claim 3,wherein R is represented by the general formula —(CF₂OCF₂)_(x)—, where xis an integer.
 5. The compound of claim 1, represented by the generalformula:

where each E_(d) is independently a moiety with the general structureR—(OCO₂—)₂, where each R is independently an aliphatic or aromaticmoiety that is optionally halogenated, E₁ and each E₂ are independentlymoieties with the general structure R′—(OCO₂—)_(i), where each R′ isindependently an aliphatic or aromatic moiety this is optionallyhalogenated and i is an integer from 2 to 6, n, m and L are integers, atleast one of L or m is a positive integer, g and h are integers from 0to 10, k is a positive integer, A is represented by the formula CY₂═C(X)—CO₂—, where Y is H or D, X is H, D, F, Cl or CH₃, each W isrepresented by one of the formulae:

where r is an integer greater than or equal to 2, each R_(f) isrepresented by one of the formulae: —CH₂(CF₂)_(t)CH₂—, —CH₂(CF₂O—(CF₂CF₂O)_(p)—(CF₂ O)_(q)]—CF₂CH₂—,—CH₂CH₂OCH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂CH₂OCH₂CH₂—,—CH₂CF(CF₃)O(CF₂)₄O[CF(CF₃)CF₂O]_(p)CF (CF₃)CH₂—where p, q and t areintegers and q can optionally equal zero.
 6. The compound of claim 1,having a molecular weight of from about 1,000 to about 10,000.
 7. Thecompound of claim 1, having a molecular weight of from about 2,000 toabout 6,000.
 8. The compound of claim 1, wherein the compound has aviscosity at 25° C. that is greater than 100 centipoise.
 9. Apolymerizable composition comprising: a photoinitiator; and apolymerizable compound including at least one fluorinated alkylene oralkylene ether moiety; at least two terminal acrylate moieties; and atleast two ester linkages which are not a subunit of an acrylate group.10. The composition of claim 9, wherein the polymerizable compound isrepresented by the general formula:

where each B₄ is independently a moiety with the general structureR—(CO₂—)₂, each R is an aromatic or aliphatic group that is optionallyhalogenated, B, and each B₂ are independently moieties with the generalstructure of R′—(CO₂—) _(i), where each i is independently an integerfrom 2 to 6, each R′ is independently an aromatic or aliphatic moietythat is optionally halogenated, n, m and L are integers, at least one ofL and in is greater than zero, each g and h is independently an integerfrom 0 to 10, each A is independently represented by the formula CY₂═C(X)—CO₂—, where Y is H or D, X is H, D, F, Cl or CH₃, each W isindependently represented by one of the formulae:

where r is an integer greater than or equal to 2, R_(f) is representedby one of the formulae: —CH₂(CF₂)_(t)CH₂—,—CH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂CH₂—,—CH₂CH₂OCH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂ CH₂OCH₂CH₂—, or—CH₂CF(CF₃)O(CF₂)₄O[CF(CF₃)CF₂O]_(p)CF(CF₃)CH₂—, where k, p, q and t areintegers and q can optionally equal zero.
 11. The composition of claim9, wherein the polymerizable compound is represented by the generalformula: (A)_(r)-D₁-(R_(f)-((D_(d)—R_(f))_(g))-D₂-(A)_(u))_(t) whereeach D_(d) is independently a moiety with the general structureR-(CH₂O—)₂, where each R is independently an aliphatic or aromaticmoiety that is optionally halogenated, D₁ and each D₂ are independentlymoieties with the general structure R′—(CH₂ O—)_(i), where each R′ isindependently an aliphatic or aromatic moiety that is optionallyhalogenated, and i is an integer from 2 to 6, A is represented by theformula CY₂═C(X)—C(O)—, where Y is H or D, X is H, D, F, Cl or CH₃, eachR is independently represented by one of the formulae:—(O)C—(CF₂)_(n)—C(O)—, —(O)C—CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂—C(O)—,or —(O)C—CF(CF₃)O(CF₂)₄O[CF(CF₃)CF₂O_(p)CF(CF₃)—C(O)—, where g, n, p, q,r, u and t are integers, with at least one of r and t being a positiveinteger and q can optionally equal zero.
 12. The composition of claim 9,wherein R is represented by the general formula —(CF₂OCF₂)_(x)—, where xis an integer.
 13. The composition of claim 8, wherein the polymerizablecompound is represented by the general formula:

where each E₄ is independently a moiety with the general structureR—(OCO₂—)₂, where each R is independently an aliphatic or aromaticmoiety that is optionally halogenated, E₁ and each E₂ are independentlymoieties with the general structure R′—(OCO₂—)_(i), where each R′ isindependently an aliphatic or aromatic moiety this is optionallyhalogenated and i is an integer from 2 to 6, n, m and L are integers, atleast one of L or m is a positive integer, g and h are integers from 0to 10, k is a positive integer, A is represented by the formulaCY₂═C(X)—CO₂—, where Y is H or D, X is H, D, F Cl or CH₃, each W isrepresented by one of the formulae:

where r is an integer greater than or equal to 2, each R_(f) isrepresented by one of the formulae: —CH₂(CF₂)_(t)CH₂—,—CH₂(CF₂O—(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂CH₂—,—CH₂CH₂OCH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]CF₂CH₂OCH₂CH₂—,—CH₂CF(CF₃)O(CF₂)₄O[CF(CF₃)CF₂O]_(p)CF(CF₃)CH₂—, where p, q and t areintegers and q can optionally equal zero.
 14. The composition of claim9, wherein the photoinitiator is present in an amount of from about 0.5%to about 5%, and the polymerizable compound is present in an amount offrom about 1% to about 99.5%.
 15. The composition of claim 9, whereinthe polymerizable compound is present in an amount of at least 5%. 16.The composition of claim 9, wherein the polymerizable compound ispresent in an amount of at least 10%.
 17. The composition of claim 9,wherein the polymerizable compound is present in an amount of at least20%.
 18. The composition of claim 9, wherein the composition has aviscosity of at least 100 centipoise at 25° C.
 19. The composition ofclaim 9, wherein the polymerizable compound has a molecular weight offrom about 1,000 to about 10,000.
 20. The composition of claim 9,wherein the polymerizable compound has a molecular weight of from about2,000 to about 6,000.
 21. A compound having a core moiety; and at leasttwo fluorinated alkylene or alkylene ether moieties, each fluorinatedalkylene or alkylene ether moiety being linked to the core moietythrough an ester or carbonate linkage, each fluorinated alkylene oralkylene ether moiety having an acrylate moiety linked thereto.
 22. Thecompound of claim 21 having the formula R[CO₂—R_(f)—O₂CC(X)═CY₂]_(n),wherein R represents the core moiety; R_(f) represents the fluorinatedalkylene or alkylene ether moieties; X is H, D, Cl, F or CH₃; Y is H orD; and n is an integer between about 2 and about
 4. 23. The compound ofclaim 22 wherein R has the structure

each R_(f) includes a perfluorinated polyether; and n=3.
 24. Thecompound of claim 23 wherein R has the structure

each R_(f) includes a perfluorinated polyether; and n=2.
 25. Thecompound of claim 23 wherein R has the structure

each R_(f) includes a perfluorinated polyether; and n=4.
 26. Thecompound of claim 21 wherein the core moiety includes an aromaticmoiety.
 27. The compound of claim 21 wherein at least one alkylene oralkylene ether moiety is selected from the group consisting of—CH₂(CF₂)_(t)CH₂—, —CH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂CH₂—,—CH₂CH₂OCH₂CF₂O—[(CF₂CF₂O)_(p)—(CF₂O)_(q)]—CF₂CH₂OCH₂CH₂—, and—CH₂CF(CF₃)O(CF₂)₄O[CF(CF₃)CF₂O]_(p)CF(CF₃)CH₂—, where k, p, q and t areintegers and q can optionally equal zero.
 28. The compound of claim 21wherein at least one alkylene or alkylene ether moiety includes aperfluorinated polyether.